Tadahiro Sakuta1, Yasunori Tanaka1,Makoto Katsuki1 and Takamasa Ishigaki2
1Department of Electrical and Computer Engineering, Kanazawa University, Kanazawa 920-8667
We have newly designed a thermal plasma system which can be operated with a pulse modulated mode for the control of plasma power in the time domain and for creating non-equilibrium effects such as fast heating or quenching of the plasma to produce new functional materials at a high rate. The system consists of a solid state power supply with a maximum peak power of 30 kW(20 kW continuous), an induction plasma torch with a 13-turns coil of 55 mm diameter and 85 mm length and a vacuum chamber. The pulse modulated plasma was successfully produced at a plasma power of 11 kW and a pressure from 27 kPa to 101 kPa (from 200 to 760 Torr). The on and off time were each 5 ms, which corresponds to a duty factor of 50%. Measurements were carried out on the time variation of the spectral lines emitted from the ArI species. The dynamic behavior of the plasma temperature in an on-off cycle was estimated by the Boltzman plot method as an average value for eight emission lines. The excitation temperature of the ArI atom changed periodically from 5000 K to 14000 K during the cycle at 27 kPa. The magnitude of this temperature change was weakened at higher pressure of 101 kPa. The minimum duty factor to sustain the pulse modulated thermal plasma was found to be 30%, which corresponds to the pulse off time of 10 to 12 ms.
(Received August 24, 1998; In Final Form November 27, 1998)
induction thermal plasma, pulse modulation, non-equilibrium effect, fast quench, time constant
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